Generally, a battery charger is an electronic assembly comprising electrical, mechanical, and/or electronic components that together perform multiple functions associated with delivering electrical energy to a battery.
Battery charging is carried out in existing devices in several different ways, including linear dissipative voltage regulators, various types of thyristor regulators, and various types of switchmode regulators. Many existing (commercial) battery chargers are transformer type thyristor-controlled battery chargers that are larger and heavier than switchmode type battery chargers. Existing battery chargers including switchmode type battery chargers usually have a poor power factor (i.e., a ratio of real power flowing to the load to an apparent power in the circuit), and therefore draw more input current than necessary and have a non-sinusoidal AC input current.
Existing battery chargers may provide: reverse polarity protection; jumper selectable output voltage (e.g. twelve-volt or twenty-four volt charging); automatic charge cycles; temperature compensation; electromagnetic interference (EMI) filtering; surge protection (protection from unwanted transient electrical energy coming from the AC power source attached to the battery charger); alarm relays; fuses for overcurrent protection on the AC input and the DC output; power factor correction; configuration of the charger via a digital interface; battery charging algorithms; electromagnetic emission control and immunity; alarm systems with low power consumption latching relays; and/or an LCD battery charger status display. However, many existing battery chargers have no reverse polarity protection, no thermal protection, no alarm relays, no text display, no digital communications interface, no microprocessor, no capability to select twelve volt and twenty-four volt operation in the same charger, no capability to charge a zero volt battery, etc.
Some existing battery chargers use mechanical adjustment devices such as potentiometers, dual in-line package (DIP) switches, pushbuttons, slide switches or other adjustment mechanisms that have a high risk of failure, intermittent functionality, or wear.
Some existing devices' “housekeeping power supplies,” which power on-board control circuitry, are only supplied from DC battery power and therefore cannot function if a battery is not connected. As a result, some existing battery chargers may mistake a “zero-volt battery” (a battery which has never been charged or which has been deeply discharged and therefore has very low voltage across its battery terminals) for a short circuit and therefore will not initiate battery charging, and/or may be unable to operate due to lack of housekeeping power from the zero-volt battery.
In addition, certain types of battery applications are subject to regulatory mandates by the National Electric Code, the National Fire Protection Association, and Underwriter's Laboratories regarding when and how the batteries must be charged. Specifically, regulations require lead-acid starting, lighting, and ignition batteries (SLI batteries) that are used to start emergency generators or diesel fire pumps to be continually “float” charged, ensuring that the batteries are fully charged and ready for service at all times. The static battery chargers used to float charge SLI batteries also provide direct current to power accessory loads in the form of equipment such as, for example, electrical switchgear and/or the supervisory systems necessary for the generator or fire pump systems to function.
Traditional continuous float charging involves round-the-clock charging in which the battery charger alternately outputs two charging voltages to the SLI battery to be charged: a “float” voltage and a “boost” fast-recharge voltage. The float voltage is output approximately 99% of the time and is intended to maintain the battery in its fully charged state by replenishing charge at the same rate the battery self-discharges (e.g., up to approximately 13.3 to 13.8 volts for a 12-volt battery). The boost voltage is applied only intermittently and is intended to quickly charge a zero-volt battery that has never been charged or recharge an existing battery that has undergone a discharge event (e.g., approximately 15.5 volts for a 12-volt battery). The boost charge is employed only for the limited duration necessary to fully charge the battery, after which the output voltage from the charger returns to the float voltage pending the next discharge event.